The present study evaluated whether the unilateral 6-hydroxydopamine (6-OHDA) model of Parkinson's disease produces autonomic deficits. Autonomic parameters were assessed by implanting a small radiofrequency telemetry device which measured heart rate variability (HRV), diurnal rhythms of heart rate (HR), core body temperature (cBT) and locomotor activity (LA). Rats then received 6-OHDA lesion or sham surgery. 6-OHDA lesioned rats exhibited head and body axis biases, defective sensorimotor function (“disengage” test), and prominent apomorphine rotation (all P < .05 versus controls). Diurnal rhythm of HR was lower for 6-OHDA lesioned rats (n = 8) versus controls (n = 6; P < .05). Whilst HR decreased similarly in both groups during the day, there was a greater decrease in HR for the 6-OHDA lesioned rats at night (by 38 b.p.m. relative to 17 b.p.m. for controls). LA and cBT did not differ between surgery groups. This study indicates the unilateral 6-OHDA model of PD shows subtle signs of cardiovascular autonomic dysfunction.

Performing stressful procedures in view of cage mates may cause stress in observer animals. However, it is not known if stressful procedures performed in close proximity to, but not in view of cage mates are stressful for the (observer) cage mates. Radiotelemetry and postmortem in vitro studies of the vas deferens were used to determine the effects of stress on observers. Heart rate (HR) and core body temperature (cBT) were recorded for 1 h following weighing of a cage mate or 1 h during restraint of a cage mate and the hour following return of the restrained mouse to the cage. This procedure was repeated daily for 15 days. HR and cBT were increased in observers during both restraint and weighing of cage mates. Analysis of the area under the curve showed that HR and cBT in observers were significantly higher during restraint of a cage mate than after weighing of a cage mate. When mice were returned to the cage after weighing or restraint, HR and cBT were significantly higher in the cage mates of restrained animals. Comparison between days 1, 3, 7 and 14 found that, as the experiment progressed, HR and cBT were significantly reduced in the observer mice during the hour following return of the cage mates after restraint. Results from previous studies have shown that chronic stress causes the vas deferens to become hypersensitive to exogenous application of noradrenaline (NAd). In this study, vas deferens from observers of restraint had a significantly increased response to NAd. These results indicate that stressful procedures should be conducted in isolation from other mice.

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Implantable telemetry devices are widely used in experimental animals. We investigated the potential for such implants to induce stress in mice. Changes in body weight and post-mortem responses of the vas deferens to noradrenaline (as a measure of sympathetic activation) were measured 28 days after transmitter implantation. We examined the influence of the anaesthetic used during implantation (pentobarbitone or fentanyl/fluanisone/midazolam), the strain (Balb/c and CBA) and the body weight at the time of implantation (small = 19–24g; large = 27–30g). A sham-implantation procedure did not significantly affect the responses to noradrenaline. When telemetry transmitters were implanted in small mice of both strains, there was a significant increase in the maximum response to noradrenaline compared to that obtained in tissues from large mice. The anaesthetic used during implantation did not affect the responses to noradrenaline obtained post mortem. Mice of both strains had a significant post-operative weight loss and this was maintained for the experimental period. The results show that implantation of telemetry transmitters has a significant impact in mice that weigh < 25g.

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